Optical Networks

Optical Networks

2008

Topics

• Optical Links – Light Sources, Detectors and Receivers

– Optical Fiber Channel

– Optical Amplifiers

• Digital Optical Communications – Time and Wavelength Multiplexing

– Optical Cross-Connects (OXC)

• Optical Networks – First Generation Optical Networks and SONET

– Second Generation Optical Networks

• Multi Protocol Lambda Switching

• DWDM optoelectrical metro network

Review of Optics

• What is a monochromatic wave

• Polarization of light

• Interaction between Light and Matter

Total Internal Reflection and Absorption

• Diffraction

• Interference

Light Sources

• LED -- Light emitter diodes

• Laser diodes

• Single mode laser diodes

Detectors and Receivers

• Solid state detectors

• PIN diode

• Circuit noise and signal to noise ratio in a

receiver

• Direct detection and bit error rate

• Avalanche photodiodes (APD)

Detectors and Receivers (cont.)

Optical Fiber Channel (1) • Total internal reflection in a optical fiber

• Telecommunications industry uses two windows:

1310 & 1550 nm

– 1550 window is preferred for long-haul

applications (Less attenuation, Wider window,

Optical amplifiers)

Optical Fiber Channel (2)

• Multimode fibers and their limitations

Optical Fiber Channel (3)

• Single mode fibers and limitations

• Non-linearities in fibers

• Coupling light in a fiber and connecting

two fibers

Fiber Amplifiers erbium doped fiber amplifiers (EDFA)

Semiconductor Optical Amplifiers (SOA)

Topics










Digital Optical Communications

• Signal Quantization / Coding: from analog to

digital signal and vice versa

• Digital Modulation: Amplitude, Phase, and

Frequency Modulation

• Multiplexing to increase the bandwidth of an

optical channel

– Time Division Multiplexing

– Wave Division Multiplexing (WDM)

• WDM vs. DWDM

Digital Optical Communications (cont)

DWDM

1310/1510 nm

1310/1510 nm

16 uncorrelated wavelengths

λ1 λ2 λ3 λ4 λ5 λ16

2.488 Gbps (1)

2.488 Gbps (16)

16*2.488 Gbps = 40 Gbps

1530-1565 nm ramge

16 stabilized, correlated

wavelengts

Fiber Optics Transmission

Optical Switch • 1-input 2-outoput illustration with four

wavelengths

• 1-D MEMS (micro-electromechanical system) with dispersive optics

–Dispersive element separates the ’s from inputs

–MEMS independently switches each

–Dispersive element recombines the switched ’s into outputs

1-D MEMS

Micro-mirror

Array

Digital Mirror

Control

Electronics 1011

Wavelength

Dispersive Element

Input Fiber

Output Fiber 1

Output Fiber 2

Input & Output fiber

array

All-Optical Switching

• Optical Cross-Connects (OXC)

–Wavelength Routing Switches (WRS)

– route a channel from any I/P port to any O/P port

• Natively switch s while they are still multiplexed

• Eliminate redundant optical-electronic-optical

conversions

DWDM

Fibers

in

DWDM

Demux

DWDM

Demux

DWDM

Fibers

out

DWDM

Mux

DWDM

Mux

All-optical

OXC

Optical Add-Drop Multiplexor (OADM)

OADM

1

2

3

1

2

’3

’3 3

Wavelength () Converters (WC)

improve utilization of available wavelengths

on links

needed at boundaries of different networks

all-optical WCs being developed

greatly reduce blocking probabilities

No Wavelength converters

1

2 3

New request

1 3

With Wavelength converters

1

2 3

New request

1 3

WC

Topics










Optical Networks

• 1 st Generation: optical fibers substitute copper as

physical layer

– Submarine Systems

– SONET (synchronous optical) in TDM

– FDDI for LAN, Gbit Ethernet etc.

• 2 nd Generation: optical switching and

multiplexing/ WDM

– broadcast-and-select networks

– WDM rings

– wavelength routing networks

• 3 th Generation: optical packet switching???

Big Picture

SONET

Data

Center SONET

SONET

SONET

DWD

M DWD

M

Access

Long Haul Access

Metro Metro

SONET

• Encode bit streams into optical signals

propagated over optical fiber

• Uses Time Division Multiplexing (TDM) for

carrying many signals of different capacities

–A bit-way implementation providing end-to-end

transport of bit streams

–All clocks in the network are locked to a

common master clock

–Multiplexing done by byte interleaving

Practical SONET Architecture

ADM – Add-Drop Multiplexer

DCS – Digital Crossconnect

Protection Technique Classification

• Restoration techniques can protect network against:

– Link failures

• Fiber-cables cuts and line devices failures

– Equipment failures

• OXCs, ADMs, electro-optical interface.

• Protection can be implemented

– In the optical channel sublayer (path protection)

– In the optical multiplex sublayer (line protection)

• Different protection techniques are used for

– Ring networks

– Mesh networks

Path Switching:

restoration is handled

by the source and the

destination.

Normal Operation

Line Switching: restoration

is handled by the nodes

adjacent to the failure.

Span Protection: if

additional fiber is available.

Line Switching:

restoration is handled by

the nodes adjacent to the

failure.

Line Protection.

Path Protection / Line Protection

Shared Protection

1:N Protection

• Backup fibers are used for protection of

multiple links

• Assume independent failure and handle

single failure.

• The capacity reserved for protection is

greatly reduced.

Normal Operation

In Case of Failure

Protection in Ring Network

1+1 Path Protection

Used in access rings for traffic aggregation

into central office

1:1 Line Protection

Used for interoffice rings

1:1 Span and Line Protection

Used in metropolitan or long- haul rings

(Unidirectional Path

Switched Ring) (Bidirectional Line

Switched Ring)

Protection in Mesh Networks

Working Path

Backup Path

• Network planning and survivability design

– Disjoint path idea: service working route and its

backup route are topologically diverse.

– Lightpaths of a logical topology can withstand

physical link failures.

Trend: IP over DWDM

• IP is good for routing, traffic aggregation, resiliency • ATM for multi-service integration, QoS/signaling • SONET for traffic grooming, monitoring, protection • DWDM for capacity

IP over DWDM: Why? • IP and DWDM => Winning combination

– IP for route calculation, traffic aggregation,

protection

– DWDM => Cheap bandwidth

– Avoid the cost of SONET/ATM equipmnt

• IP routers at OC-192 (10 Gbps)

=> Don't need SONET multiplexing

• Optical layer for route provisioning,

protection, restoration

• Coordinated restoration at optical/IP level

• Coordinated path determination at optical/IP

level

MPS • MPS = Multi-Protocol Lambda Switching

– MPLS + OXC

– Combining MPLS traffic eng control with OXC

• All packets with one label are sent on one wavelength

• Next Hop Forwarding Label Entry (NHFLE)

– <Input port, > to <output port, > mapping

DWDM Summary

• DWDM => Switching Bottleneck => O/O/O

switches

• High speed routers => IP directly over DWDM

• Data and control plane separation => IP

Control Plane

• Data will be circuit switched in the core

• IP needs to be extended to provide addressing,

signaling, routing, and protection for

lightpaths

• High-speed point-to-point Ethernet => LAN-

WAN convergence

Telepnonecompany

Cable TVcompany

Satellite dish

Satellite dish

Copper pairtelephone line

Coxial cable(75 O)

The Current Home Service System

Internet Router for modemconnections

Internet Router for cablemodems

To telephonebackbone

To cable TVnetwork

To the Internet

To the Internet

Satellite dish

Satellite dish

Coxial cable(50/75 O)

Multip-ServiceCompany

Sigle modeFiber cable

The Optoelectrical Multip-Service System

To telephonebackbone

To the Internet

To cable TVnetwork



Why Optical Networks?

DWDM optoelectricl metro network

Optical Networks

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